The course is devoted to the most important technologies of joining materials for power engineering, especially their welding. The course includes brief theories of welding processes, weldability of materials including methods of its evaluation. Additionally, the treatment of materials prior to welding, the treatment after welding are included in the course (preheating of materials, including methods of preheating, controlled cooling after welding, post-welding heat treatment). Subsequently, the types and methods of welding are described, especially arc welding (manual arc welding, automatic or semi-automatic flux-core arc welding and its variants, use of protective gases, materials for electrodes, etc.). Attention is also focused on defects of welded joints, their definition and evaluation of admissibility, as well as methods of evaluation of welded joint quality in terms of occurrence of defects, respectively in terms of their structure and properties. Particular attention is paid to the welding of materials in power industry, where the properties of welded joints change during the high temperature exposure, and to the associated limitation of welding processes and combinations of different steels.